package simulation;

public class convert {
    public String convert(String s, int numRows) {
        // 处理⼀下边界情况
        if (numRows == 1) return s;
        int d = 2 * numRows - 2, n = s.length();
        StringBuilder ret = new StringBuilder();
        // 1. 处理第⼀⾏
        for (int i = 0; i < n; i += d)
            ret.append(s.charAt(i));
        // 2. 处理中间⾏
        for (int k = 1; k < numRows - 1; k++) // 依次枚举中间⾏
        {
            for (int i = k, j = d - i; i < n || j < n; i += d, j += d) {
                if (i < n) ret.append(s.charAt(i));
                if (j < n) ret.append(s.charAt(j));
            }
        }

        // 3. 处理最后⼀⾏
        for (int i = numRows - 1; i < n; i += d)
            ret.append(s.charAt(i));
        return ret.toString();
    }
}

